FI106300B - Process for manufacturing lignocellulose-based composite products - Google Patents

Description

106300

METHOD FOR PREPARING LIGNOCELLULOSE-BASED COMPOSITE PRODUCTS

The present invention relates to a process according to the preamble of claim 1 for the preparation of lignocellulose-based composite products, such as sheets and molds, and for the improvement of their properties, in particular their dimensional stability and strength properties.

According to such a method, the finely divided lignocellulosic material is mixed with a modification chemical and a binder to produce a moldable mixture, and then said mixture is brought to the desired shape.

Wood, due to its light weight, its beautiful appearance, its heat-insulating properties and other good properties, is well suited as a building material. However, wood has properties that limit its use. These include e.g. susceptibility to biological damage and humidity.

It is known that by modifying the main components of wood, namely lignin, cellulose and hemicellulose, the properties of wood and the like, such as straw, flax, jute and bagasse, and products derived therefrom can be improved. The use of organic acid anhydrides for the modification of lignocellulose-based materials has been studied for several decades. The most common anhydride used for this purpose is acetic anhydride, which was used to treat sawdust and wood flour as early as 1928 (Fuchs 1928). Later, this chemical has also been used to modify solid wood (Goldstein et al. 1961). In the simplified acetylation process (Rowell et al. 1986), the lignocellulose-based material is treated with acetic anhydride, followed by heating the material at 120 ° C for various lengths of time.

Also known are solutions in which wood material is treated with maleic anhydride (MAH) dissolved in glycerol.

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There are certain drawbacks to prior art. Thus, both acetic anhydride and glycerol-dissolved MAH are liquid products whose use includes e.g. causes difficulties with finely divided fiber or powder material. The fibers curdle, requiring a separate process to separate them after treatment.

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It is an object of the present invention to overcome the drawbacks of the prior art and to provide a novel solution for improving the properties of lignocellulosic based boards, molds and other similar composite products.

The invention is based on the idea that the lignocellulosic based material is modified in the solid phase. In this case, the solid state modifying chemical is mixed with the lignocellulose-based material and the binder to form a homogeneous mixture which can be shaped, for example, into a sheet or such a fiber composite, which is cured by heat. During the heat treatment, the modification chemical reacts with the lignocellulosic material-15 to form bonds thereto. In the present invention, in particular, powdered anhydrides (e.g., maleic or succinic anhydride) or their solid starting materials are used as the solid state modification chemical to modify the fibrous or filamentous lignocellulosic material.

More specifically, the method according to the invention is essentially characterized by what is stated in the characterizing part of claim 1.

The invention provides considerable advantages. Thus, the present solution can significantly reduce the thickness swelling of sheets containing lignocellulosic fibers and increase their transverse tensile strength. These things also come to light '; from the following application example. It should also be noted that the modification effectively prevents the binding of water molecules to the cell wall components of the wood. Although the pores of the fibers may contain water, the reduced moisture content of the cell wall itself, as well as the resulting "closed cell wall structure", contributes to the inhibition of the enzymatic activity of the 30 fungi. Thus, the invention can improve the decay resistance of products containing lignocellulose.

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The invention will now be explored in greater detail by means of a detailed description and an application example.

In the description and example, reference is made to the accompanying figures, of which Figure 5 shows a flow chart for a particle board manufacturing process; Fig. 4 shows the effect of the resin and modifier on the transverse tensile strength of the sheet made of MDF fibers and Fig. 5 shows the effect of the resin and modifier on the thickness swelling of the sheet made of MDF.

15 Definitions and Composition Components:

The lignocellulose-based material used in the process of the invention is e.g. wood fiber, cellulose fiber, wood flour, wood chips and / or fibers of annual or perennial plants. The wood raw material is preferably "" finely divided ", which means that the wood flour has a particle size of about 0.01 to 10 mm, preferably about 0.05 to 5 mm.

The wood fibers and wood chips also have a cross-sectional or corresponding thickness of about 0.01 to 10 mm, preferably about 0.05 to 5 mm, and a length of about 1 to 200 mm, preferably about 5 to 100 mm.

According to a preferred embodiment, suitable wood or cellulosic fibers are prepared by grinding a lignocellulosic feedstock. The abrasive grinding effect is achieved, for example, by mills with grooved blades, such as plate or conical grinders.

Examples of suitable materials are wood material for use in the manufacture of fibrous products, such as wood fibers for MDF boards, cellulosic fibers from mechanical pulp production, recycled pulp fibers and sawdust. Wood and cellulose fibers are particularly preferred.

4 106300 "Lignocellulosic" material may be derived from wood, eg spruce, pine birch or wound, or annual or perennial plants. Thus, straw, flax, hemp, jute, reed, reed and bagasse are also suitable as starting materials.

In the context of the present invention, "wood composite products" include particle board and fiber board as well as moldings and so-called non-woven products.

According to the invention, an organic "acid anhydride solid at least at room temperature" is used to modify the lignocellulosic material. Suitable hap-10 anhydrides include, for example, maleic and succinic anhydride and phthalic anhydride. Solid starting materials for the compounds, such as malic, fumaric and maleic acids, are also suitable for processing, since they generally produce the desired anhydrides during heat treatment of the product.

A "binder" of a composite is a liquid or solid that binds other components of a composite. Most preferably, a binder which, like an acid anhydride, is in solid form at room temperature to provide a solid phase process. It is known that many binders / adhesives for use in the form of aqueous solutions have been solidified to facilitate their shelf life and transport. In the context of the present invention, binders of this kind can in most cases be dry blended with the fibers. The solid binder may be in the form of powder or fibers. Typically the binder used is a phenolic, urea or melamine based resin or a lignin or mineral based binder, isocyanate, starch, casein or gluten. Particularly suitable resins are, for example, phenol-formaldehyde resin, urea-25 maldehyde resin, melamine-formaldehyde resin, vinyl resins such as polyvinyl chloride and ABS copolymers, styrene-butadiene resin, poly styrene, acrylic acid resin, polyester stearate, polyester stearate, polyester stearate, polyester. Urea-formaldehyde is used as a binder for ordinary particle boards and the like, while phenolic or urea melamine resins are typically used for bonding particle boards for humid conditions.

In addition to or instead of said binder, a suitable thermoplastic, 5 106300 thermosetting resins or a mixture thereof may also be used. Thus, as an example of the latter alternative, a mixture of a thermoplastic and a phenolic, urea or melamine based resin may be mentioned. wherein the thermoplastic comprises from 1 to 99% by weight of the blend and the resin from 99 to 1% by weight. Affordable. are, for example, mixtures of phenolic resin and polypropylene in a ratio of 1: 10 to 10: 1.

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Polyolefin such as polyethylene or polypropylene is particularly preferably used as a plastic binder, but other types of plastic binder such as polyesters (e.g., polyalkylene terephthalates, PET, PBT), polylactide and so-called polyethylene glycol may also be used. bicomponent fibers having a lower temperature melting plastic material than 10 core parts. Recycled plastic grades can also be used. The plastics are preferably used as fibers or chips to easily be mixed with the lignocellulosic component. Therefore, the recycled thermoplastic is torn before being mixed with the lignocellulosic material.

According to a preferred embodiment, fibrous starting materials are used, i.e., a lignocellulosic feedstock and a binder, including plastics, of the same fiber length. The lengths of the fibers are preferably from about 0.1 mm to about 100 mm, typically from about 0.5 mm to about 50 mm. In this case, classification of the mixture can be avoided and thus at least substantially homogeneous mixture 20 produced. This option is particularly suitable for the production of non-woven carpets. By using a fibrous thermoplastic as a binder, which fibers are on average longer than the fibers of the lignocellulosic material, non-woven products can be made.

25 Manufacture of products: *

The moldable mixture is extruded into a sheet or mold or formed into a non-woven product. The invention can be used to make finished products which are cured to the desired shape, but can also be applied to the preparation of intermediates, preforms, etc., whereby the resulting products are in uncured form.

According to a preferred embodiment, the sheet or mold extrudate is post-processed 106300

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at room temperature.

One application of the modification is the manufacture of fiberboard and particle board and flakeboard. These include HDF and MDF (High and Medium Density Fiber 5 Board) and OSB (Oriented Strand Board).

An embodiment of the chipboard manufacturing process according to the invention is illustrated in more detail in Figure 1. According to such a process, suitable wood chips (e.g. softwood and / or leaf chips) are first screened, whereby the raw material is divided into three parts. Kar-10 chips are used to make the middle part of the particle board, while the finest part is used to form the surface layer. The roughest part of the screening, sticks, impurities and the like, are removed as waste. The screened chips and the chips, respectively, are processed separately from each other until hot pressed to form the desired chipboard. The chips and chips are ground, dried, screened and stored as shown in the figures. Adhesive (= binder) and optional excipients such as paraffin (dispersion of paraffin), ammonium chloride, tetramethylenehexamine or que bracho are then added to the chips and the like. The latter three agents can be used mainly to control the properties of binders / adhesives.

After the binder is added a powdery modifier, which is uniformly mixed with the fibrous material. For the addition of binder, excipients and modifier, a gluing drum or similar device with a blender with blades may be used. Typically, the moisture content of the chips or chips is less than 10% when mixed with a powdered anhydride modification chemical or a corresponding acid-25 starting material. After the addition of the anhydride, the fractions are pooled and sprinkled on a suitable support, e.g., tape. The scattered pulp, i.e. the mixture of fibers, chips and / or chips, modifier and binder, is compressed into a sheet using parameters suitable for the sheet dimensions and materials (compression temperature, compression time, etc.). The board is shaped eg by sawing. The waste is removed and the desired size flat products are recovered.

The effect of the anhydride or similar modifying agent as a board improver is enhanced when the board is post-treated at a temperature above room temperature (> 60 ° C-106,600 ° C, preferably about 70 ° C-150 ° C). The duration of the post-treatment varies with temperature and can be performed after hot pressing before or after sawing. One option for post-treatment is to extend the heat-pressing time by 1.1 to 10 times.

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It should be noted that in the above process, liquid binders may be used in place of solid binders. The liquid binder is then added to the wood or fibrous components, allowed to dry if necessary, and a solid modifier added. However, unless the moisture content of the wood or fibrous components rises excessively, they need not be dried prior to further processing; indeed, with absolutely dry wood, anhydrides may react less well than with a few percent (typically 0.1-5 wt%) moisture.

According to the invention, preferably 50 to 90% by weight of lig-15 nocellulose-containing material, 1 to 30% by weight of a modifying chemical and 5 to 40% of binder are used for making the plates.

As stated above, the modification method is also suitable for the so-called. for the production of molds. In this case, synthetic fibers and natural fibers are added in the manufacture of preforms, such as fiber mats and preforms, to which powdered anhydride and, in some cases, adhesives have been added. The molds are post-heat-treated as are plate-like products. The molding compositions typically comprise: 50 to 90% by weight of a lignocellulosic material, 1 to 30% by weight of a modifying chemical and 5 to 40% of a binder.

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The invention also provides a process for making a non-woven product using a fibrous thermoplastic as a binder. The function of thermoplastic in non-woven products is to bind the non-woven carpet without vibration. Tying at the carpet production stage is done either by "knitting" or by partial melting of the thermoplastic.

The following embodiment illustrates the invention in more detail.

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Example

Composite sheets were made by blending the lignocellulosic material, the modifying chemical and the binder, which were pressed into sheets under the following conditions: - sheet size: 400 mm x 400 mm x 4 mm - target density: 750 kg / m3

- compression temperature: 180 ° C

- pressing time: 60 s / mm 10

After pressing, the plates were treated for 2 hours at 170 ° C.

The binders used were powder binders: phenolic resin (Peracit 888412) and melamine-urea-formaldehyde resin (Dynomel), as well as polypropylene and polypropylene as fibrous binders. Both resin and polypropylene as such and mixtures thereof were used. The amount of resin binder was 10 wt% and the polypropylene 20 wt% based on the dry weight of the lignocellulose-based material. The blend ratio of resin to polypropylene was 1: 1 and it was added so that the blend was 20% by weight based on the dry weight of the lignocellulosic material.

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The modifying chemicals used were solid phase succinic anhydride and maleic anhydride as well as liquid phase acetic anhydride and a mixture of maleic acid glycerol (MG / ethanol) dissolved in ethanol. The concentration of the maleic acid-glycerol mixture in the ethanol solution was 20% and the solution was added to the fibers so that the concentration of the maleic acid-glycerol mixture in the fibers was 15% based on the dry weight of the fibers.

Comparative experiments were also conducted in which no anhydride was used at all.

The sheets were determined for the products' flexural strength, elastic modulus, transverse tensile strength and thickness swelling. The results are shown in Figures 1-4.

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As shown in the figures, the addition of succinic anhydride or maleic anhydride in the solid phase reduced the sheet swelling by more than 75%. The transverse tensile strength of modified sheets increased by 45-130% compared to untreated sheets.

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Compared to acetic anhydride modified sheets, the solution of the invention resulted in a significant improvement in all four of these parameters when polypropylene alone was used as the binder.

Modification with maleic or succinic anhydride of the invention improved the elastic modulus of the boards from a few percent to about 25%. Compared to the reference plates, the strength and swelling properties of the modified plates were significantly improved when polypropylene (PP) alone was used as the binder. In a way, anhydrides have an adhesion promoter effect on adhesion between natural fibers and PP. Male-15 tartaric anhydride modification slightly reduced the flexural strength of the sheets when phenol-formaldehyde resin (PF) or a mixture of PF and PP was used as the binder, while marine succinic anhydride modification had a positive effect on flexural strength.

Claims (20)

A process for the preparation of lignocellulosic composite products, according to which process 5. finely divided lignocellulosic material is mixed with a modifying chemical and a binder to form a moldable mixture, and then - said blend is brought into the desired form or a solid starting material for such is used as a modifying chemical, and - a thermoplastic or a mixture of a thermoplastic and a thermosetting resin is used as an adhesive. 2. A process according to claim 1, characterized in that an acid anhydride or a corresponding acid, which is solid at least at room temperature, is used as a modifying chemical. 3. A process according to claim 1 or 2, characterized in that maleic anhydride or succinic anhydride is used as a modifying chemical. 20 Method according to claim 1, characterized in that the product is cured after the modification treatment. Process according to any of claims 1-3, characterized in that wood particles, such as wood fibers, wood clips, wood powders, cellulose fibers, wood wool, or fibers of one or multi-annual plants, such as cellulosic material, are used. Process according to any of the preceding claims, characterized in that, in addition to the thermoplastic, a binder which is fixed at room temperature is used. > 30 7. A process according to any one of claims 1 to 5, characterized in that, in addition to the thermoplastic, a binder which is in liquid form at room temperature is used. H 106300 8. A process according to claim 6 or 7, characterized in that phenol-, urea-, melamine- or isocyanate-based resin is used as a binder. Method according to claim 1, characterized in that recycled thermoplastic is used as thermoplastic adhesive. 10. A process according to claim 1 or 9, characterized in that polyethylene, polypropylene, polyester or polylactide is used as a thermoplastic binder. 10 11. A method according to claim 1, 9 or 10, characterized in that the thermoplastic is used in the form of fibers, pits or buckles. 12. A method according to claim 1.9, 10 or 11, characterized in that the recovered thermoplastic is ripped off before being mixed with the lignocellulosic material. 15 A process according to claims 1 or 7-12, characterized in that a mixture of thermoplastic and phenol-, urea-, isocyanate- or melamine-based resin is used as a binder, wherein the thermoplastic portion of the mixture is 1 - 99% by weight, and the resin part of the mixture is 99-1% by weight. 20 Process according to any of the preceding claims, characterized in that the lignocellulosic material is added to the binder at the same time as the modification chemical. 25 15. A process according to any one of claims 1 to 13, characterized in that the ligno cellulosic material is added to the binder prior to the modification chemical. . Process according to any of the preceding claims, characterized in that 50-90% by weight of lignocellulosic material, 1-30% by weight of modifying chemical and 5-40% by weight of binder are mixed together. Process according to any of the preceding claims, characterized in that the moldable mixture is pressed into a disc or a molded product. 106300 18. A method according to claim 17, characterized in that the post-processing or molding of the product is post-treated at a temperature higher than the room temperature or by prolonging the vapor pressing time. 5 Method according to any of the preceding claims, characterized in that HDF, MDF or OSB are produced. 20. A method according to any of claims 1 to 17 for the manufacture of a non-woven product, characterized in that fibrous thermoplastic is used as a binder. • * 9 · «m